FABRICATION OF OCULAR PROSTHESES*

When the surgical site is well healed and dimensionally stable, fabrication of an ocular prosthesis can begin. Before beginning, a thorough examination of the enucleated socket must be made to ensure proper healing and the absence of infection. The location of the implant, movement of the tissue bed, and size and extent of the socket should be noted.

Impressions :

An impression of the socket can be with irreversible hydrocolloid. An impression tray can be fabricated from hard baseplate wax by warming it over a flame and adapting it to the contour of the area around the eye. A wax handle is attached to aid manipulation. The tissue side is scored with a hot spatula to afford retention for the impression material. The patient is seated erect, requested to stare at a distant spot, and instructed to hold his gaze in a straightforward position with eyes open while the impression is being made. This procedure will ensure that the posterior aspect of the enucleated socket and its rectus muscles will be in the same relative position as those of the remaining eye.

The irreversible hydrocolloid is mixed using an extra half measure of warm water, providing a smooth, runny mix that will set quickly. The impression material is placed into a large syringe. Enlarging the opening of the tip of the syringe will facilitate expression of the impression material. With the patient’s eyelids open, the irreversible hydrocolloid mixture is injected into the socket, being careful to completely fill the socket without trapping tiny air pockets. The lids are then released and some of the impression material is expressed over the lids. The tray, which has been coated with the impression material, is placed over the eye and allowed to set. When set, the material in the socket and over the lids can be, removed as one piece. The patient is instructed to open his eye as wide as possible, and the impression is gently removed. Care must be taken not to tear the impression from the tray at the thin section that represents the lid opening. Prior to pouring the cast, this section of the impression can be reinforced by placing a straight pin through it from the posterior aspect. The impression is inspected and the socket is checked for any residual irreversible hydrocolloid.

Formulation of the cast :

The impression is poured in two sections. A box is formed around the tray with 3-inch masking tape. The first half of the cast is poured with a mix of dental stone using “slurry water” to accelerate the setting time. This procedure will prevent excessive water loss from the impression. The mix is vibrated onto the boxed impression up to and around the widest part of the socket impression. The impression is then placed in a humidor while the stone sets. At least two keyways are cut into the surface of the first pour using a large, round vulcanite bur. The stone is then lubricated with a separating medium and the second half of the impression is poured and returned to the humidor. 

Fabrication of the sclera:

            After the stone has set, the mold can be separated by removing the wax tray and  impression material.  With the aid of a laboratory  knife the lid opening of the mold is enlarged to allow molten wax to be poured into it without having the wax congeal before the mold is filled. Soaking the mold in warm water for a few minutes and blotting the excess water will allow the wax to flow and fill the mold without adhering to the stone.

            After the wax has cooled, the mold is opened and the wax pattern is recovered. The ridge of wax that represents the lid opening is trimmed away, the anterior surface of the pattern is contoured into a smooth hemispheriod. The posterior surface will reflect the topography of the tissue bed of the eye socket. Close adaptation of the posterior surface to the corresponding tissue bed produces movement in the eye prosthesis in harmony with natural eye. Close adaptation also reduces fluid collection behind the prosthesis that could produce irritation and foster bacterial growth.

            The wax pattern is now tried in the eye socket and the lid contours are evaluated. To insert the wax prosthesis, the upper lid is lifted and the superior edge of the prosthesis, the upper lid is lifted and the superior edge of the prosthesis is placed up and under the lid. Then, while drawing the lower lid down, the lower border of the prosthesis is seated. The  wax pattern should  feel comfortable to the patient but may cause mild irritation and tearing. The wax will not move as freely as the finished acrylic resin prosthesis. The eye contours and lid openings  are checked from several angles.

            When appropriate contours have been developed the wax pattern is ready to be invested. Either a denture flask or a crown and bridge flask may be used. White orthodontic stone is preferred to avoid possible contamination of the scleral white or clear acrylic resin with the pigments from yellow dental stones. After filling the lower half of the flask with dental stone, some of the stone mixture is vibrated onto the posterior surface of the wax pattern. Gently the wax  pattern is laid on top of the stone in the flask, being careful not to trap air. After the stone has set, the exposed stone is lubricated  with a separating medium and the upper half of the flask is filled. When the stone has set, the flask  may be separated by gently prying it apart. No boilout is necessary. The wax pattern is removed from the mold, and the mold is washed with soap and water to remove residual separating medium. A  coat of foil substitute is applied  and the mold is ready to be packed by the compression method.

            The material used in packing the mold is scleral white acrylic resin. It is available commercially* or can be made by combining 1.5gm of zinc oxide powder with 100gm of clear acrylic resin. By processing the resin at 150°F for 9 hours and at 212° F for 2hours, the possibility of porosity is reduced.

            The acrylic resin sclera is recovered from the flask and the flash removed with rotary instrument and polished with wet flour of pumice. Using a wet rag wheel at low speed will prevent burning of the acrylic resin. The sclera should be brought to a high shine and washed with soap and water. The acrylic resin sclera is inserted and the contours and lid opening are verified again. Necessary adjustments are made at this time. If any grinding is performed, the sclera must be polished before it can be returned to the eye.

           Iris location.The iris location is determined with the sclera in place and the patient standing in a relaxed position. Again the patient is instructed to look at a distant point. By comparison with the natural eye, the center  of the pupil of the prosthesis is located and marked with a pointed applicator stick dipped in waterproof ink. The sclera is then removed. By placing the point of an architect’s compass at the pupil center, a circle is scribed the same diameter as the natural iris. Water proof ink the used for this  circle. The size and location of the iris must match that of the remaining eye. This is easily verified by sight and by measuring with a millimeter rule using the inner canthus and inner edge of the limbus as  points of reference.  Another factor to be considered at this time is the location of the iris in relationship to the opening of the lid. Usually the upper lid covers a portion of the upper half of the iris, whereas  the lower border of the  iris rests at  or slightly above the lower lid.

            The sclera is then reinvested in the same manner as the wax pattern. Reinvestment facilitates handling as the sclera must be cut down for incorporation of the iris. The anterior  surface is also reduced to allow tinting of the sclera. The sclera material removed for these purposes is easily replaced with clear acrylic resin.

            Before reinvesting the sclera, a piece of 28-gauge casting wax is positioned over the circle that represents the iris. A warm wax spatula is used to remove the excess wax from outside the circle and, the same time, to seal the wax to the sclera. When flasked, the wax will leave a depression in the stone of the flask in the position of the iris. This depression is deepened approximately 2 mm at the center and then tapered toward the sides to form a smooth, rounded concavity. This concavity will produce the corneal prominence in the finished prosthesis. This area can be contoured to capture highlights of reflected light to correspond to the natural eye and to produce a more lifelike appearance.

The next procedure is the “cutdown” for placing the iris painting. A diamond wheel or mounted stone with a square edge accomplishes this task smoothly and easily. Acrylic resin is removed to a depth of 3 to 5 mm depending on the thickness of the sclera. A carbide inverted cone bur will flatten the floor of the cutdown and will also undercut the walls around the edges. When painted, this undercut will show through the sclera and produce the effect of the limbus. A limbus can also be produced by carefully tinting the surface of the sclera or the iris.

The sclera is again inserted into the socket *** verify that the floor of the cutdown is parallel to the plane of the body and perpendicular to the line of sight. When the floor of the cutdown is an correct alignment, the anterior portion of the sclera is reduced by at least 1 mm. the sclera is reduced substantially around the iris location allowing a depth of 1 to 1½ mm above the floor of the cutdown. The edge of the iris cutdown is kept at a sharp angle.

The sclera is now ready to be tinted. A cotton applicator stick with a ball of beading wax at each end serves as a handle while tinting. A sclera in children is usually blue. In light-skinned adults it is lighter blue or green. With darker-skinned individuals the sclera tends to be darker, showing tints of brown-orange. A light yellow pigment is applied to the canthus area, except in children. Blood vessels an be either painted on or simulated by red rayon or cotton fiber applied to the sclera and held in place with a clear acrylic resin spray. If necessary the iris cutdown is painted to represent the limbus.

The sclera is then returned to the lower half of the flask and the iris painting is positioned in the cutdown. Now the prosthetic eye is ready to be packed with clear acrylic resin. Care must be taken to avoid trapping air between the iris painting and the acrylic dough. A thin mix of clear, cold-cure acrylic resin is flowed over the iris and sclera and cured in a pressure pot before the clear, heat-cure acrylic resin is packed.

After the curing process the eye is recovered from the flask, finished, and polished. At delivery, the prosthesis should be verified for correct size, lid opening, and contours. At this time it is important to note the high-lights in the natural eye and those of the prosthesis. These highlights should match as closely as possible. If not, selective grinding on the corneal surface of the prosthesis will change the position of the highlights.

Iris illustration with acrylic paints on watercolor paper disks.The colors most often used are titanium white, ultramarine blue, burnt sienna, yellow ochre, cadmium yellow, and alizarin crimson. Greens should be avoided as they become very vivid when incorporated into acrylic resin. To simulate green, shades of olive should be used. Black India ink is needed for a purple color. The paints are mixed with water to a heavy consistency. If the mixture is too thin, a true color will not be obtained and the paints will tend to flow together. Only a small amount of paint should be mixed at a time inasmuch as the paint dries quickly.

Cold-pressed watercolor paper of imperial grade is used. Paper disks are cut in 0.5mm graduations, ranging from 10.0 to 12.0mm. Paper disks are cut in 0.5mm graduations, ranging from 10.0 to 12.0mm. Paper punches with exact rounds are desirable to avoid ragged edges in the finished prosthesis. A disk of correct size is glued to a strip of paper of the type from which the disk was cut. This strip will provide a handle and will simplify the handling of the small disk during painting. It also provides a convenient place to test paint mixtures.

There are five basic parts to an iris painting : the pupil, the base color, the detail, the collarette, and the limbus. The pupil is painted first and is located in the center of the iris disk. A circle of the correct size is drawn on the disk with black India ink and then filled in. The size of the pupil is judged by shading the natural eye with the hand and observing the variation in the size as it is exposed to light. Usually the average of the extremes will produce a pupil of acceptable size.

The first step in painting the iris is the base color. The base color is the darkest color that can be observed in the natural iris and is usually blue, brown, olive, gray, or a combination of these colors. This coat is applied in a heavy layer using brush strokes to ensure that the disk is completely converted. The iris is developed in layers going from darker colors to lighter colors. Thin radial strokes form the striations and give an illusion of depth. The brush point should be very fine so that delicate striations can be produced. A small area around the pupil is left unpainted. This will later be painted to conform of the collarette. When dry, the paint shade used for the iris should be a shade darker than the iris that is being matched inasmuch as these paints have a tendency to lighten and brighten after they have been processed. Viewing the paints when wet or covered with a drop of water will help in marching shades. The collarette is then painted and is usually a little brighter than the base color. Finally the limbus is added. This can be painted on the iris side but is most often painted on the undercut rim of the cut down iris on the sclera. The color used to paint the limbus is normally a shade that blends the iris painting to the sclera.

Although acrylic paints are the most popular. Watercolors may also be used. However, watercolors are more time-consuming, as drying time must be allowed between each step of the painting to prevent the colors from running together. In addition, watercolors are not as color stable nor as long lasting as the acrylic paints.

Lris illustration using oil paints on acetate disks,The colors of oil paint used are ultramarine, cerulean blue, cadmium red deep, cadmium yellow, cadmium orange, burnt sienna, burnt umber, black, and titanium white. There are two methods of using oil paint when painting iris disks. The first employs a mono-poly solution (acrylic monomer thickened with clear polymer) as a thinning and curing agent. The paints are applied to performed black acetate disk that is covered with a corneal button of clear acrylic resin. The second method uses linseed oil as a paint thinner.

Iris painting using mono-poly.Mono-poly is made by combining ten parts heat-cure acrylic monomer to one part clear acrylic polymer by weight. To combine the monomer and the polymer a pan of water is heated and brought to a light boil. The monomer is then poured into a Pyrex beaker. The beaker is placed in the pan of boiling water and when the monomer is warm, the polymer is sifted slowly into the monomer while stirring continuously with a glass rod. Two viscosities of this solution are required. After about 10 minutes the solution attains the viscosity of a light oil. Most of this solution is then poured into a dark glass bottle and stored. The remaining portion is returned to the boiling water until the mixture reaches about twice the viscosity of the first mixture. The second mixture is also stored in a dark glass bottle. The thinner of the two solutions is used as the thinning and curing agents for the oil paint, whereas the thicker one is used to adhere the painted iris disk to the corneal button.

In this method the pupil is incorporated into the corneal button. Therefore no consideration of pupil size or location is required during the iris painting. The paint is applied to the disk in a manner similar to the method previously described. The paint for the base coat is mixed and thinned with mono-poly and applied to the disk with heavy brush strokes that cover the entire disk. Several layers of paint are applied until the disk is well covered and a striated effect is achieved. The painting of the iris is completed in the same manner using the lighter shades to match those of the remaining iris. The collarette is painted last and is applied in a starburst pattern around the center of the disk. The corneal button is placed on top of the painted disk to verify the size and location of the collarette. Adjustments in its size or location can be made at this tie. The limbus is painted around the edge of the disk in a shade that will suitably blend the iris painting into the sclera. The painted iris disk is checked for color accuracy against the natural eye by placing a drop of water on the painted iris.

The iris painting is attached to the corneal button by applying a coat of the thicker mono-poly to the contacting surfaces and gently sliding them together, being careful not to trap any air bubbles between the surfaces. When in correct alignment, the two sections are pressed together and allowed to dry.

To obtain corneal buttons with the pupil incorporated, clear acrylic resin is packed and processed into a specially prepared iris button flask. After processing, the iris buttons should not be removed from the flask. Using round burs of different sizes that correspond to pupil sizes, a hole is drilled into the button surface of the button. The button stem is visible from the bottom and is used as a guide to locate the center of the disk. The holes should be about 2 mm deep. This will be sufficiently deep to create a black pupil after the button has been finished and polished, but not deep enough to give the pupil a raised or rounded appearance when the prosthesis is viewed from the side. The holes should be dampened with monomer and packed with a clear acrylic resin that has been stained. Black the flask should be reassembled and processed. The flask is placed in cold water and slowly brought to a boil. It should boil for 30 minutes. Then it should be removed from the flask and the bottom surface of the button should be flattened by milling on a flat surface covered with a fine emery cloth. Milling will remove any black acrylic resin outside of the pupil area.

Iris illustration with oil paint and linseed oil.The method of iris illustration with oil paint and linseed oil differs only slightly from the mono-poly method. The disk used in this method is clear with a papillary hole in the center. The pupillary hole may be enlarged with a small rattail file to correspond to the pupil size of the natural eye. The easiest method of holding this type of disk is to insert the beaks of a cotton forceps, which have had a small groove cut into them, through the pupillary opening. The tension of the forceps will hold the disk in the groove during the painting process. The colors are selected and mixed using linseed oil as the thinning agent. The interior and exterior surfaces of the disk are completely covered with the base color, leaving an area around the pupil unpainted for the collarette. After the base coat is applied the disk is finished by the methods previously described.

After the iris disk has been painted it must be placed in a drying oven at 125 to 1400F for a period of 4 to 6 hours. The corneal button is now packed with clear acrylic resin in the iris button flask. The painted corneal button is placed over the acrylic resin dough and is trial packed. The flash is removed and at this time a black acetate disk is placed behind the iris painting. This black disk provides the pupil in the finished prosthesis. The processed corneal button is recovered and the flash is trimmed. The button is polished, retaining its stem.

Sclera formation.A wax pattern is obtained and contoured in the same manner as previously described. When one is satisfied with the size and shape of the wax sclera, the iris is located. The wax inside the circle is removed to a depth of 3 to 3mm and the iris button is inserted in this cavity. The wax pattern with the corneal button in place is inserted into the eye socket. Using the stem as a handle, the iris is adjusted to match the position and gaze of the natural iris. After removal of the wax sclera and iris carefully from the socket, the iris is waxed into position and the assemblage returned to the socket to verify its position. The wax pattern is then invested and processed as previously described. The stem on the corneal button will retain the button in the upper half of the flask and is correct relationship to the sclera. After the acrylic sclera is recovered from the flask, with the button incorporated, the stem is removed and the prosthesis polished. At this time the sclera is reinvested in a flask. This allows for reduction of the anterior surface and tinting. One should avoid getting paint onto the iris area when tinting. The sclera is returned to the flask and processed with clear acrylic resin.

Patient instruction.The method of inserting and removing the prosthesis and its care are demonstrated to the patient. The prosthesis should be removed at least once a day for cleaning. The prosthesis should be not be allowed to come into contact with alcohol or solvents of any kind as this could cause crazing of the acrylic resin. If the eye should become scratched it must be returned for polishing.

Modification of a stock eye prosthesis.A stock eye is selected with the correct iris size, color, and approximate sclera shape. The peripheral and posterior surfaces and reduced 2 to 3mm and retentive grooves are cut into the posterior surfaces. A small, straight stick is secured with sticky wax over the pupil perpendicular to the plane of the iris. This stick will act as a handle and also as a guide for aligning the prosthesis in the correct relationship to the natural eye.

A small amount of irreversible hydrocolloid is mixed with warm water and placed on the posterior surface of the prosthesis. With the patient looking straight ahead at a distant spot, the prosthesis and impression material are fitted between the lids and seated in the socket. Care must be taken to avoid trapping air between the impression material and the tissue surface. The handle is used to bring the prosthesis into correct alignment with the natural eye and the lids are checked for opening and contour.

The impression is removed and excess impression material is trimmed appropriately. The stick handle is removed from the anterior surface of the prosthesis. The prosthesis and impression are invested in the lower half of a flask. After the stone has set, two small projections of autopolymerizing acrylic resin are attached to the canthus areas of the prosthesis. These projections will hold the prosthesis in the upper half of the flask and retain the correct relationship between the prosthesis and the mold during the packing and processing procedures. Using a separating medium on all exposed stone surfaces, the top half of the flask is poured. The packing, processing and finishing of the prosthesis are accomplished as previously described.

 

Complications*

Ptosis.Ptosis can be divided into two major categories for the purposes of resolution by ocular prosthesis: pseudoptosis and true ptosis. Pseudoptosis occurs when the superior palpebra is not properly supported by the prosthetic eye. This simple problem is usually resolved by changing the contours of the prosthetic eye to properly support and reposition the lid.

A more difficult situation arises when a true ptosis exists. Because of inadequate musculature or lack of tissue tone, the superior lid droops over the prosthesis. Corrections of ptosis often can be accomplished surgically by shortening a muscle or reducing the volume of tissue. However, in many situations special contouring the prosthesis will alleviate the problem. Allen described a method of contouring the prosthesis to overcome ptosis. First, the upper aspect of the corneal prominence is enlarged to raise the lid. Then the superior aspect of the prosthesis is reduced to form a shelf or depressed area onto which the lid may rest and fold. A slight bulge is placed behind the lid to make it appear full.

Lower lid droop.Drooping of the lower lid sometimes can be solved in a similar manner. By removing some of the inferior aspect of the anterior prominence of the prosthesis, pressure forcing the lid down is reduced. Material is then added to the prosthesis behind the lid in an attempt to push the lid out and allow it to rise. A second solution is to recontour the inferior aspect of the prosthesis and place the pressure at the medial and lateral areas in which the lower lid has more support. The medial and lateral aspects of the inferior border are elongated and the central aspect is thinned and shortened.

Other problems.Other situations that may cause problems and that can be corrected surgically (Reen and Beyer 1976) are entropion and ectropion. Where the contours of the lower lid or position of the eyelashes leave an unesthetic appearance, careful contouring of the wax pattern or relieve the pressure on the lid and increase its support will sometimes correct the situation without surgery.

As aging occurs, patients lose tissue tone and elasticity in many areas of the body. The superior and inferior palpebra are similarly affected. Special attention must be given to contouring a prosthesis for the geriatric patient to overcome problems of tissue tone. Blepharosulcus is not uncommon and special configurations to minimize esthetic problems in aging patients may be required (Guibor, 1976).

Occasionally cicatricial bands or adhesions are found that unite the wall of the socket to the lids (symblepharon). These scar bands will reduce the mobility of the prosthesis or prevent its fabrication. Surgical revision of the socket in conjunction with a pressure appliance is sometime successful in eliminating these scar bands. In some patients ocular prostheses can be used by placing a groove into which the scar band can rest, but mobility of the prosthesis is compromised.

A contracted socket can occur after trauma or infection or when a patient does not utilize a prosthesis for a long period. The result is loss of an adequate sulcus to retain the prosthesis. To compensate for this loss, expansion of the socket can be obtained by applying pressure with an enlarged prosthesis. Progressive enlargements can be effected as time progresses. A simple shallow cul-de-sac can be accommodated by contouring the inferior aspect of the prosthesis as suggested for lower lid drooping.

Evisceration is becoming more popular as a treatment modality. In evisceration the contents of the globe rather than the entire globe are removed. An implant may or may not be used, but implantation is recommended. The cornea is often left intact. To reduce the incidence of elceration and abrasion of the cornea or possible loss of the implant, a stock prosthesis should not be used. Instead, a custom eye should be fabricated. An impression allows for fabrication of an ocular prosthesis with intimate contact on the tissue bed and distributes pressure more equally than does a stock eye.

 

 

 

 

RESTORATION OF ORBITAL DEFECTS

Fabrication of orbital prostheses that are esthetic is a most difficult challenge. Because conversation with others is initiated with eye contact, slight discrepancies in position of the eye, lid contour, and color of the prosthesis are immediately noticed by the observer. In some patients it may not be possible to duplicate the appearance and contour of the remaining normal eye and adjacent orbital structures. In orbital defects in particular, an unesthetic prosthesis creates more psychological trauma than no prosthesis at all.

Preoperative consultation is valuable in informing the patient of the nature of the defect and the choices available for restoration. Unfortunately many patients are under the impression that the prosthesis will move and function in concert with the remaining eye. Photographs of prostheses restoring similar defects are helpful in eliminating this misconception. In most patients it is not necessary to obtain preoperative photographs or impressions, for they are of little value in fabricating the postsurgical prosthesis.

Surgical resection of orbital tumors is dependent on the nature and extent of the tumor. Resections that are confined to removal of the orbital contents result in defects that are easier to restore esthetically. As the surgical margins extend beyond the orbital confines, prostheses are less esthetic because of the inability of camouflage the lines of juncture between skin and prosthesis. Additionally, as the prosthesis extends beyond the orbit, movable tissue beds may be encountered resulting in further exposure of the lines of juncture.

The surgeon should be instructed to line the bony walls of the orbit with skin. In most instances attempts should not be made to occlude the orbit with local or distant flaps of tissue. After such reconstructions, little room remains for placement of a suitable orbital prosthesis. In addition, recognition of recurrent tumor may be delayed because the margins of the resection are not clearly visible.

 

Impressions

 Accurate impressions of orbital defects are difficult to obtain because the periorbital tissues are easily displaced. Displacing tissue is particularly difficult to avoid when dealing with patients who have submitted to a total maxillectomy as well as an orbital exenteration, for the cheek area is not longer supported by bone. In these patients, the definitive obturator must be fabricated, appropriately contoured, and properly positioned before proceeding with impressions of the orbital area.

Initially, a facial moulage is obtained and from the resultant east a master impression tray is fabricated. Unless the bony undercuts of the orbit are to be engaged, the tray need not extend significantly into the orbital cavity. The purpose of the impression is to record the orbital and periorbital tissue bed as accurately as possible. To do so the patient must be placed in an upright position and extreme care taken not to displace the tissue bed. Prior to obtaining the impression, undesirable undercut areas should be blocked out with petrolatum gauze. Irreversible hydrocolloid is a suitable impression material, but other materials, such as silicone or reversible hydrocolloid, are also appropriate. The impression material is syringed into the smaller skin creases and areas of difficult access and the tray loaded with the impression material is teased gently into position. The tray is suspended in the appropriate position, taking care not to compress the tissue. When irreversible hydrocolloid is employed and additional water is added to the mix, the viscosity of the material is decreased resulting in less tissue bed compression. During the procedure the patient should keep the remaining eye open and fixed to a distant point squarely ahead. This will prevent undesirable contraction of residual lid musculature and prevent distortion of the defect. Following removal, portion of the impression may require support.